This invention relates to a zener diode for use as a discrete device and as a component in an integrated circuit. Adaptations for both bipolar transistor type and insulated gate field effect transistor (IGFET) type integrated circuits are disclosed. This invention also relates to a method of making such discrete and integrated circuit configurations.
More specifically, this invention relates to a zener diode having a very accurately predictable breakdown voltage, which can be consistently produced under commercial production conditions. It also relates to a unique device configuration which, when incorporated in an integrated circuit, shares an electrode in common with a bipolar transistor or an IGFET.
A zener diode is a solid state device having two contiguous regions of opposite conductivity type and a PN junction at the interface of the two regions. Typically one of the regions is more lightly doped than the other, and is the region chiefly affecting breakdown voltage of the PN junction. Small variations in the doping level in this latter region can produce undesirably large variations in breakdown voltage of the PN junction. Commercial diffusion practices simply are not controllable enough to avoid such small variations from one diffusion run to another. Moreover, such variations are frequently found among slices in the same diffusion run, and even across the face of a given slice. Analogously, uniformity in such lighter doping is difficult to obtain when growing monocrystalline bodies and forming epitaxial layers. This results in lower yields of zener diodes having the breakdown voltage desired. Lower yields of a device having the intended characteristics will ordinarily increase the manufacturing cost of that device. In addition, the lower yields may even make it economically impractical to incorporate that device in an integrated circuit.
I have discovered a new zener diode that is unaffected by small variations in original or diffusion doping but which is readily produced with currently available commercial production techniques. Accurately predetermined breakdown voltages can thus be consistently obtained under commercial production conditions. Moreover, my zener diodes can be readily incorporated in both bipolar transistor and IGFET integrated circuits. Thus, integrated circuits can be readily made that include zener diodes with accurately predetermined breakdown voltages. My zener diode can share an electrode and even a region in common with a transistor receiving its overvoltage protection. Such use of my zener diode is an integrated circuit reduces the number of electrode connections, as well as the integrated circuit area otherwise needed. This, of course, increases reliability and reduces cost.